Vladimir Putin may have taken Crimea for Russia, but in Washington on Wednesday the talk was of US annexation of Canada – all 4m square miles of it.

That at least was the “thought experiment” conducted by the Woodrow Wilson Center, a prestigious DC thinktank, which hosted a debate featuring the author of a book advocating political union of the two North American neighbours.

Diane Francis, a conservative Canadian newspaper columnist with dual US citizenship, says her call for the “merger of the century” has been listened to more seriously south of the border where she claims to have received complimentary letters from Hillary Clinton and Jeb Bush.

“In Canada, people are horrified,” admitted Francis, before discussing how its 13 provinces and territories could become US states – but why Quebec might instead choose to become a semi-independent commonwealth, “a bit like Puerto Rico”.

Though few, if any, of those on Wilson’s panel of experts believed it could ever happen, the whimsical nature of their debate belied more serious discussion of the merits of European-style border reform and growing talk of greater economic integration even among North American political leaders.